← ACARA Digital Technologies Years 7–8

TypeError: assignment to a constant variable

The error JavaScript shows when code tries to give a new value to a const variable. Fix it by declaring the variable with let if its value needs to change.

Part of: ACARA Digital Technologies Years 7–8 — Programming with Control Structures and Functions (JavaScript) — Module 69

Understanding TypeError: assignment to a constant variable in ACARA Digital Technologies Years 7–8

What it does: lives is declared with const, so the second line tries to change a constant and JavaScript throws a TypeError. This message is about giving a new value to a const. A missing semicolon is a different kind of problem. Use const for values that never change, like pi. A score changes during the game, so it needs let. Shorthand updates such as += and ++ also reassign a variable, so they fail on const just like = does. A TypeError also appears when you try to call something that is not a function, so check the message and what the name holds.

Common mistakes: score is given a new value on line 4, so it cannot be a const. Reassigning it gives TypeError: Assignment to constant variable. Declare it with let score = 0; instead. lives-- changes the value, but a const cannot change. This causes TypeError: Assignment to constant variable. Use let lives = MAX_LIVES; because lives changes.

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This module's key terms are also in a printable crossword (Modules 624–634) and word search (Modules 611–634).

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Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

A student writes const score = 0; then score = 10; What happens when the code runs?

TypeError: Assignment to constant variablescore becomes 10 with no error

Matches

const points = 10; points += 5;

↓

points is a const, so += tries to give it a new value and causes a TypeError. Declare it with let instead.

Applying

Meanings

Term

TypeError: Assignment to constant variable

Meaning

The error JavaScript shows when code tries to give a new value to a const variable. Fix it by declaring the variable with let if its value needs to change.

Practice

const player = 'Mia';

Testing

Gaps

score = 0;

Check Answer

Spots

2console.log(name);

3const score = 0;

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Quick Questions

1. A student writes const score = 0; then score = 10; What happens when the code runs?

A. TypeError: Assignment to constant variable ✓

B. score becomes 10 with no error

A const variable cannot be given a new value after it is created, so JavaScript stops with a TypeError.

2. Which declaration lets you change the value later without an error?

A. let lives = 3; ✓

B. const lives = 3;

Use let for values that will change, like lives in a game. const is locked after the first value.

3. The console shows: TypeError: Assignment to constant variable. What is the cause?

A. The code tried to reassign a const variable ✓

B. The code forgot a semicolon at the end of a line

This message is about giving a new value to a const. A missing semicolon is a different kind of problem.

4. Which code will cause a TypeError?

A. let total = 5; total = total + 1;

B. const total = 5; total = total + 1; ✓

total = total + 1 gives total a new value. This is fine with let but fails with const.

5. How do you fix this code? const count = 0; count++;

A. Change count++ to count--

B. Change const to let ✓

count++ changes the variable, so it must be declared with let. Using -- would still change a const and fail.

Match the Pairs

TypeError: Assignment to constant variable. → The error JavaScript shows when code tries to give a new value to a const variable.

let score = 0; score = 5; → A variable declared with let can be given a new value, so no TypeError happens.

Reassigning a const variable causes a TypeError → const lives = 3; lives = 2;

Fix the error by changing const to let when the value must change → let lives = 3; lives = 2;

const points = 10; points += 5; → points is a const, so += tries to give it a new value and causes a TypeError. Declare it with let instead.

const name = "Sam"; name(); → name holds a string, not a function, so calling it with () causes a TypeError. Only call names that are functions.

Key Term

TypeError: Assignment to constant variable

The error JavaScript shows when code tries to give a new value to a const variable. Fix it by declaring the variable with let if its value needs to change.

Fill in the Blanks

1. let score = 0; score = score + 5;

Hint: Type the keyword that declares a variable whose value can be changed later.

2. const lives = 3; lives = 2; // Error type: TypeError

Hint: Type the name of the error JavaScript shows when you reassign a const variable.

3. const name = "Sam"; name(); // TypeError: name is not a function

Hint: Type the variable name that the error message says is not a function.

4. const lives = 3; lives = 2; // TypeError: Assignment to constant variable

Hint: Type the word from the error message that describes the kind of variable that cannot be reassigned.

5. const PI = 3.14159; console.log(PI);

Hint: Type the keyword used for a value that should never change.

Spot the Error

Question 1

A const name = "Ava";

B console.log(name);

C const score = 0;

D score = score + 10;

Line C — score is given a new value on line 4, so it cannot be a const. Reassigning it gives TypeError: Assignment to constant variable. Declare it with let score = 0; instead.

Question 2

A const MAX_LIVES = 3;

B const lives = MAX_LIVES;

C lives--;

D console.log(lives);

Line B — lives-- changes the value, but a const cannot change. This causes TypeError: Assignment to constant variable. Use let lives = MAX_LIVES; because lives changes.

Question 3

A let count = 0;

B const limit = 3;

C while (count < limit) {

D limit += 1;

E }

Line D — limit is a const, so adding to it causes TypeError: Assignment to constant variable. The loop should update the counter that changes, count += 1;

Question 4

A const price = 5;

B price = price + 2;

C console.log(price);

Line A — price is changed on line 2, so a const will throw TypeError: Assignment to constant variable. Use let price = 5; for values that change.

Question 5

A const age = 12;

B console.log(age());

C console.log(age + 1);

Line B — age holds a number, not a function, so the brackets () cannot call it. JavaScript shows TypeError: age is not a function. It should be console.log(age);

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